This invention relates to container closures and it particularly relates to sealing washer pre-assemblies for container closure systems.
One application of the present invention is known as a polygonal base flange closure system. The components of an exemplary prior art container closure system of this type are shown in exploded, perspective view by FIG. 1 to comprise an insert 10, generally of coated mild steel, having an internally threaded, tubular body 12 with a radially outwardly extending flange 14; the flange having an polygonally shaped periphery 16. The insert fits into a collar 18 formed in a wall 20 of a metal, such as mild steel, container 22 and the container wall 23 around the collar has a complimentary shape to the flange periphery, to prevent the insert from turning in the collar. An elastomeric flange sealing washer 24 fits about the insert body 12 on the insert flange 14 and is trapped and compressed to seal between the insert and the container wall, when the upper part 26 of the insert has been curled over the collar rim 28. An externally threaded plug 34, with an elastomeric plug washer 36 is screwed into the insert body to seal and close the container. The whole closure may be closed by an anti-tamper cap 38 crimped over the insert curled upper part 26.
The elastomeric flange sealing washers 24 of such type A closure systems are prone to leak when a filled container is dropped, especially when the dropped container lands on the closure; the insert 10 being forced inwards relative to the container wall 20, which decompresses the flange sealing washer 24. In drop tests in accordance with paragraph 9 of The United Nations “Recommendations on the Transport of Dangerous Goods”, container closures of the above described type tend to fail when the container is dropped from heights of 2 meters or lower and the closure is positioned during the drop test such that the drop impact fold line in the container wall (e.g. drum top) runs across the closure.
A solution to this problem is described in Document U.S. Pat. No. 5,853,100 (Kars), wherein an additional flange sealing washer is radially compressed between the insert and the collar, the additional flange sealing washer being of a resiliently deformable elastomeric material that, when compressed, has a lower coefficient of friction with regard to the coated or uncoated mild steels of the insert and collar than other types of flange sealing washer materials, such as white EPDM rubber. These material characteristics of the additional flange sealing washer enables it both to be positioned and compressed in the correct position between the collar and the insert and to remain compressed and in position in the event that the insert is forced inwards relative to the container wall; thereby maintaining an effective seal between the insert and the collar. When subjected to the same UN drop test there were no failures for container closures fitted with the above described additional flange sealing washer.
In spite of its technical superiority over conventional container closures there are major problems with the use of this additional flange sealing washer, mainly because of quality control and efficiency in the automatic assembly of flange sealing washers with inserts. Inserts fitted with two flange sealing washers are produced and sold as a combination, together with other components, to container manufacturers who form the collars and fit the closures to the containers; using purpose-designed closure insertion tools.
Document U.S. Pat. No. 3,208,775 (Stap et al) discloses a closure seal with an “additional protecting ring 15 made of a compressible or deformable material having a high resistance to aggressive fluids, solvents, detergents and the like, such, for example as polyethylene or other suitable thermoplastic materials” (column 2, lines 43 to 46). Document U.S. Pat. No. 3,946,894 (Simkus) discloses a “resilient sealing gasket 18” (column 2, line 47). Document GB 1 392 603 A (Drums Ltd.) discloses “Sealing gaskets, an ‘O’ ring 4 and a plain cylindrical ring 5, both of rubber” (see page 2, lines 9 and 10). Document FR 2 755 723 A (Phoenix France) discloses a coextrusion of a base EPDM and a mixture of polyvinyl chloride and nitrile butadiene to form a sliding facing 20 on a glass mounting joint. Document FR 2 520 467 A (Comnind Spa Azienda Ages) discloses a rubber vehicle window seal 10 co-extruded with a foam rubber sealing flange 20.
The system by which a flange sealing washer is typically fitted to a flanged insert on the assembly lines of a closure manufacturer comprises conveying each insert sequentially past two washer loading stations, which can each deliver a washer to and fit and stretch it over the tubular body of an insert so that the washer lies in contact with the insert flange. The second washer delivery station is provided to guard against miss-feeds, being arranged to fit a washer to an insert in the event that the first station fails. For closures in accordance with our above International Patent Specification, the second washer delivery station is employed to fit the additional washer. As this additional (second) washer differs in configuration and material to the original washer, each delivery station has to meet different assembly parameters resulting in a non-interchangeability of parts and equipment and some assembly failures; as inserts can come off the assembly line without one or the other or both washers. With this additional requirement of different washer assembly operations, the manufacturing efficiency of closures in accordance with Document U.S. Pat. No. 5,853,100 (Kars) tends to be reduced.
For an additional washer, an intensified quality control system is required to assure that the additional washer is always present and at its design position.
A solution to this assembly problem would be the use of a single flange sealing washer having the necessary compressibility/friction characteristics and indeed such a single flange sealing washer is described in Document U.S. Pat. No. 5,853,100 (Kars), but this single flange sealing washer has a complex cross-section, it is L-shaped, and has to combine the high compressibility and low co-efficient of friction characteristics in the one material. The cross-sectional shape is more expensive to produce and more complicated to assemble automatically. Also, being of a single material, such flange sealing washers are generally not universally compatible with all container contents and thus limit the use of the container to which they are fitted. From a logistics point of view it is much preferable to have a nearly universally useable flange sealing washer and a consequentially nearly universally useable container.
The elastomeric plug washers 36 do not normally leak in such UN drop tests. However, the elastomer of which the plug washer is made has to be related to container contents; an elastomer/content combination that causes the elastomer to swell is unacceptable as this would prevent a plug from being properly refitted. Thus, conventional prior art plug washers have, for example, used black nitrile rubber for mineral oil contents and EPDM for chlorinated hydrocarbons, foodstuffs etc.
A major problem with the plug washer in another application known as a serrated base flange closure system is that, due to its design of a large, flat, unenclosed washer, a much higher closing torque is required than for the polygonal system plug washers; 50% or more. Expensive elastomers such as VITON® are required to cope with container contents and torque loads. Costs are further increased because of the larger cross-sectional size of serrated system plug washers.